Tune in to "John King, USA" Monday night at 7 ET for live reports from Baton Rouge, Louisiana. Floodgates upriver have been opened and the swollen Mississippi is threatening thousands along its banks.

Krotz Springs, Louisiana (CNN) -- The Nolan family spent the last few days packing up their belongings, moving out furniture, helping relatives and praying for a miracle in the face of the rising, menacing waters of the Mississippi and Atchafalaya rivers.

By Sunday, they had a few things they still had to do: clear out their trailer home in the Halphen Hollow subdivision of Krotz Springs, Louisiana, in order to head to higher ground ahead of the 5 p.m. mandatory evacuation deadline, and find a way to celebrate their daughter Mayah's fourth birthday.

So, after all the frantic last-minute preparations were complete, Jake Nolan finally made it to a nearby grocery store to get a cake. It was in hopes of giving Mayah a little bit of sunshine during what her father has described as a terrifying experience.

"She can't swim, and she hears all the stories about the water rising," Jake Nolan said. "She is scared she won't be able to make it out."

The Nolans aren't alone. They are among 750 people in low-lying areas around Krotz Springs who were ordered to leave after the U.S. Army Corps of Engineers authorized the opening of floodgates on the Morganza Spillway.

The aim is to minimize greater devastation further downriver, in cities like Baton Rouge and New Orleans. But the consequence is that as many as 4,000 people, according to Louisiana Gov. Bobby Jindal, could have their homes submerged as waters are funneled into the Atchafalaya River Basin, between that river and the Mississippi.

That includes the town of Krotz Springs, about 20 miles southwest of Morganza. This area is the first with a significant population seeing the rising water after this past weekend's opening of four floodgates at the Morganza Spillway.

Jake Nolan said Sunday that he, his wife and their three children moved into the subdivision two months ago. Now, they are frantically preparing to move out -- heading to Jake's sister's house until the floodwaters recede.

"We just moved in here, and now we're in the process of moving everything out," said Nolan, 23. "I have no choice. If not, I'm going to lose everything."

Handling the logistics of a last-minute move is one thing. But as challenging is explaining what's happening, and why, to a young child. Nolan said his daughter Mayah has "heard the stories of the snakes and the alligators and everything else that's liable to come up the river."

"She doesn't really understand," her father said.

Brett Ansley, a Krotz Springs native, is also trying to come to grips with the Corps' decision that has turned his life upside down.

By day, he's an inspector at an oil refinery, checking pipes and welding. But now he has put that and everything else on hold, as he hitched up his trailer home to his truck in order to head to higher ground.

Asked about the approaching waters, the first words that sprang to Ansley's mind were "crazy" and "unreal."

"It's a lot of water that's going to be coming around here," the 24-year-old said.

His great-grandmother was in Krotz Springs for the great flood of 1927, which inundated 165 million acres, killed 246 people and left another 600,000 homeless throughout the Mississippi River system, according to a National Weather Service report.

That flood, ironically, spurred the creation of the Corps of Engineers, empowering them to create systems to guard against further calamities -- and giving them the authority to let waters flow from some levees to wash away some areas in order to spare others. This, of course, is what's happening with Krotz Springs, Melville and other communities nearby.

Ansley recalls his grandfather, too, telling him about the historic 1937 flood. The family stuck around the southeastern Louisiana community, but he's not sure what will happen when the floodwaters finally subside this time around.

"I don't know who's going to come back, who's going to stay gone," he said. "It won't be the same. I'd like to come back, but we'll have to wait and see what happens."